It has previously been proposed to make ignition coils for multi-cylinder internal combustion engines in such a way that a primary leg of the coil has a pair of primary windings secured thereto. The primary leg is coupled, magnetically, to two parallel shunt magnetic portions, each one having a secondary winding wound thereon. An air gap is placed in the shunt magnetic portions. The primary windings are selectively controlled by breaker switches--which may be transistors--in such a manner that the ignition instant for spark flash-over from the secondary windings occurs at different times. A common current source is provided for the primary windings and the respective interrupter or breaker switches. The windings are magnetically so coupled with each other that, upon interruption of current in one of the primary windings, the voltage induced in only one of the secondary windings is sufficient for flash-over of a spark at the respective associated spark plug. Such a coil is described, for example, in the referenced U.S. Pat. No. 4,233,949.
The air gaps in the secondary or shunt branches require a substantial amount of electrical energy to be transferred into magnetic energy in order to generate effective sparks at the spark plug.